Evidence for a placento-insular axis in the rat fetus

Rat pups delivered by caesarian section one day before term, either remained attached to (experimental group) or were separated from their placenta (control group). Both groups were transferred into an incubator and their metabolic parameters studied. In the control group, plasma amino acid concentration fell from 11.2 to 6.9 mmol/1, plasma insulin fell from 151 to 45 mu U/ml and blood glucose fell from 3.5 to 2.6 mmol/1 during the first hour of extrauterine life. In the breathing feto-placental units, plasma amino acid concentration remained at its birth level, plasma insulin remained high (109 mu U/ml) causing rapid hypoglycaemia (1.63 mmol/1). An immediately postnatal glucagon and corticosterone surge was visible only in the experimental group. A partially purified placental extract (molecular weight 6000 to 30000) stimulated insulin secretion in vivo (fasted adult rats) and in vitro (isolated neonatal islets). It is concluded that the placenta maintains fetal hyperinsulinaemia by creating fetal hyperaminoacidaemia and, possibly, by secreting a beta cytotropic factor.